Two-stage carburetor



TWO STAGE CARBURETOR Filed April 27 1942 3 Sheets-Sheet l Elmer 0/5012 'INVENTOR,

INVENTOR March 9, 1943. E. OLSON TWO STAGE CARBURETOR Filed April 27. 1942 :s Shets-Sheet 5 Elmer Olson Patented Mar. 9-, 1943 airs!) v STATES PA'l OFFICE o TWO-STAGE'CARBURETOR ElmerjOlson, Detroit, Mich, assignor to George M. Holley and Earl Holley Application April 27, 1942, Serial No. 440,674

, I A v i h 3 Claims. (01.26.1-23) The object of invention is to ii'nprovethe operation of two-stage carburetors in which the second. stage is brought into action when the velocity of air through the first stage reaches acertain critical value.

Inithe operation of these two-stage carburetors, certain difficulties have arisen: First, there has been a tendency for the inactive carburetor to cause the active carburetor to lean out, because it is usual to use a common float chamber and acommon fuel metering system for the. two stages,

'and the inoperative fuelnozzle bleeds air into the "operative one. Secondly, there has been a tendency for the engine to surge with such a fuel system, for the same reason. Thirdly, it is desirable that the operator have some control on the operation of the second stage, that is to say, that the second stage should.- not become operative until the throttle is almost wide open. For example, it is desirable not to open the second stage under these circumstances: atwo-stage carburetor is usually made so that the capacity is greater than asingle carburetor would be on the same engine: The low speed metering and operation would not be so good with the increased capacity. The second stage is set so asto open at wide open 5 throttle beyond the critical low suction range.

At the same air flow part throttle the second stage would open too soon and destroy the beneficial effects of high velocities, etc.

The momentthe throttle is closed, or even-partially closed, the automatic means controlling the second stage are therefore prevented from operating. Finally, when the throttle is closed, I utilize elevation taken Fig. 1 when the throttle is partly open showing the position of the controlling valve.

means for the primary venturi l2.

Fig. 6,"showing the accelerating means for the secondary venturi it.

Fig. 9 is a partial elevation on the plane 9+9of Fig. 6, showing a corresponding accelerating In Fig. 1, i is the air entrance; l2 mary venturi of the first stage carburetor, which is in operation at all times; I3 is the primary nozzle that supplies fuel to the venturi I2 is the secondary venturi and is therefore theventuri of the second stage carburetor; I5 is the second- 'ary' nozzle discharging fuel therein; I6 is the 2 ation at all times.

manually operated throttle shaft; I1 is the throttle for the first stage carburetor mountedthereon. i8 is the automatically operated throttle shaft and I9 is the throttle for the second stage carburetor. 20 is the manually operated throttle lever which is also connected to the fuel pump required for the acceleration of the engine. The lever 20 controls the throttle'shaft' l6 and the throttle l1, and therefore controls the flow of air through the primary venturi i 2 whichis in oper- The flow of air through the venturi l2 and a valve 29 (Fig. 2) integral with the throttle shaft l8 Jointly controls the opening and closing of the throttle I92" Both carburetors deliver mixture to an exhaust heated inlet mani 2 mean. t

The automatically controlled throttle shaft II is controlled by the lever 2| connected through a link 22 with the bell crank lever 23 with the'plnf 24 connected to the diaphragm 2-5. .The throttle i8 is thus maintained in the closedposition'by a I spring 26. The chamber 21 to the left of the diaphragm 25 is connected through a pipe 28 with the cylindrical valve 29 (see Figs. 2, 4 and 5).

The valve 29 has in it 'a passage 3| and admits through this passage the inlet manifold suction derived from a passage 32 communicating with the mixture outlet to the chamber 21 adjacent to the diaphragm 25 when the throttle is closed. There is a pipe 28 which connects the chamber 21 with the valve 29.

It will be seen that when the throttle is closed (Fig. 2) and when the throttle is partly open (Fig. 4) the inlet manifold suction is admitted to the chamber 21 so as to be operative upon the left Fig. 5 is a similar section showing the throttle almost wide open, showing the position of the controlling valve.

Fig. 6 shows a plan view looking down.

Fig. 7 shows a cross-sectional on plane l-'l of Fig. 6.-

Fig. 8 is a partial elevation on the plane 8--8 of elevation taken I hand side of the diaphragm 25, thereby supplementing the action of the spring 26 and keeping the throttle l9 closed. During this period the pressure on the right hand side of the diaphragm 25 is practically atmospheric.

When the throttle is almost wide open, that is to say, in. the position shown in Fig. 5, atmospheric pressure is admitted through an opening is the pri- 33 and through a passage 34 in the valve 29 to the pipe 28. This atmospheric pressure is admitted to the chamber 21 located on the left hand side of the diaphragm 25. Under these circumstances, the spring 26 is the only force holding the throttle I9 closed. When this condition arises a multiplication (2 to 1)- of the suction in the venturi I2 becomes operative. This suction is derived from a small venturi 35 located between the venturi I2 and the venturi I4, which communicates with the throat of the venturi I2 and this increased suction is transmitted through a passage 35 from the throat of the venturi 35 to a chamber -'31 located on the right hand side of the diaphragm 25. Assuming that the suction thus created in the throat of the venturi 35 is great enough to overcomethe spring 26, the diaphragm 25 is then moved to the right carrying with it the pin 24 which raises the link 22 and the throttle I9 opens.

MAIN FUEL SYSTEM (Figs. 2, 3, 6 and 7) The normal fuel supply enters from a float chamber 58 through the drill orifice 38 into a well 39 in which there dips a low speed tube 48 which communicates with an inclined low speed passage H in the bridge 42 which supports the nozzle I3. This passage communicates with a corresponding inclined passage I I in the right leg of the bridge which communicates with a vertical passage 43, which discharges through openings 44 and -45 located adjacent to and on opposite sides of the upstream lip of the throttle I1 when the throttle I1 is in its closed position, this being the usual method of supplyingrthe low speed fuel. The main fuelflows out of the well 39 through a passage 46 to the main nozzle I3 where it receives air througha plug 41, which plug also communicates through a small passage 48 at the point in the low speed fuel passage 4III at the place where it makes a 90 turn. All these are known elements of a well known carburetor.

When the engine is in operation it happens that when the throttle is wide: open and the engine is under a heavy load, means must be provided to give a little extra fuel. The means disclosed in U. S. Patents 1,575,877 and 2,835,636 is the preferred means for securing this result. This means includes a valve 49 (Fig. 1) which is located within the float chamber 58 and is held open by a spring 55 and permits fuel to to close the throttle I1.

flow through an opening 5I- to a chamber 52.

This chamber 52 is separated from an air cham-' ber 53 by means of a diaphragm 54, which, when subjected to suction in the chamber 53, moves the valve 49 against the spring 55. The chamber 53 communicates through the passage 56 with the mixture outlet on the engine side of the two throttles (Fig. 3). Fuel flows through openings. in the walls of the chamber 52 to a restricted chamber 53 transmitted through the passage 55 disappears, and hence thevalve 49 opens, fuel is admitted through the restriction 51 to the well 39, supplementing the fuel which the well 38 receives through the plug 38. At the same time,

fuel is admitted to a well 58 through the restriction 58, which passage is somewhat larger than the restriction 51. The check valve 68 normally closes the passage 59 and prevents fuel flowing from the well 58 to the well 39 which I have discovered disturbs the fuel metering characteristics of the nozzle system 46, 39, 38, of the primary carburetor I2, I3, I1, even when air is not drawn down the well 58. A surge of fuel between the two wells 39 and 58 takes place in the absence of the check valve 68.

When the throttle I9 is opened, suction is created in the small nozzle I5 which is supported by the bridge 52 and causes suction in the inclined passage 63 which transmits suction to the well 58. The ball 88 is raised off its seat and fuel enters 58 flowing up passage 63, and is discharged through the venturi I5 into the throat I4. A small air bleed 64 admits air to the fuel discharged through I4.

It is also desirable to modify the accelerating means to avoid discharging fuel through the venturi I4 when the throttle I1 is opened at a relatively slow rate when it is desired that the throttle I9 remains closed. Fig. 8'shows the accelerating means for the venturi I2 of the primary carburetor in which the throttle 28 is shown connected to a link 65 which carries a pin 66 connected to an L-shaped element 61 which engages with a solid link 68 and compresses a spring 69 which propels the piston 18 downwardly into the chamber 1I. Fuel is admitted from a float chamber 58. past the check valve 5| on the up-stroke of the piston 18, that is to say, when the throttle lever'28- is moved On opening the throttle I1, by moving the manually controlled throttle lever 28, the spring 69 is compressed, the piston 18 gradually descends and fuel passes through a passage 12,- past a check valve 13, into one leg of a V-shaped element '14. The fuel passes out of the small opening 16 directed enough to open the check valve 11, in which case the engine will normally accelerate fast enough so that by the time any fuel has a chance to accumulate on the closed throttle I9, the diaphragm 25 will be moving to the right, the

throttle I9 will be opening so that there will be no inconvenience due to the sudden discharge of fuel into the mixture outlet.

The link is connected to the throttle lever 28 by means of the pin'19 and alternative openings are sometimes'provided in which the pin 19 can be inserted and the stroke of the piston 18 varied.

In normal (economical) operation of the carburetor no fuel at all is discharged through the' opening 15, the throttle I1 being opened slowly enough so that the check valve 11 is never unseated.

What I claim is:

1. In a carburetor having a primary stage and a secondary stage, each having a Venturi mixing chamber, a fuel nozzle in each venturi, a mixture outlet for each mixing chamber, a throttle in each mixture outlet, each controlling the flow.

automatic means comprising a chamber, a moving wall therein dividing said chamber into two parts, a passage connecting one part with the suction in the throat of the venturi of the first stage so as to reduce the volume of said part by the moving of said wall, yieldable means opposing said movement, a valve controlled by said manual throttle, a suction passage connecting said valve with the other part of the chamber, a passage in said valve, a valve seat, a part thereimsaid port communicating with the mixture outlet on the engine side of the throttle, the passage in said valve being adapted to place the mixture outlet in communication with said suction passage to supplement said yieldable means in opposing said movement of said wall,

.a second port in said valve seat, said port and valve being adapted toadmit atmospheric pressure through said suction passage to said chamber when said manually operated throttle approaches the wide open position, said atmospheric pressure cooperating with the suction in the throat of the first stage venturi, linkage connecting said moving wall with said throttle of said second stage whereby the secondary throttle is held shut by the suction in the mixture outlet, when the manually controlled throttle is shut and is automatically opened by the suction in the venturi of the first stage when the manually operated throttle approaches the wide open position and when the engine runs above the speed required to create a predetermined suction in the venturi of the primary stage.

2. A device as set forth in claim 1 in which there is a fuel supply chamber common to both fuel nozzles, a continuously open passage communicating fuel to the nozzle supplying the primary venturi of the first stage, a second fuel passage controlled by a valve responsive to mixture outlet suction adapted to supply fuel to said nozzle when the mixture outlet suction falls below a predetermined value, a passage connecting said second fuel passage to the nozzle in said second venturi, and a check valve in said passage for the purpose described.

3. A device as set forth in claim 1 in which there is an accelerating fuel pump responsive to the operation of the manually controlled throttle,

two fuel outlets from said accelerating device, one outlet being adapted to discharge fuel into the primary venturi, the other outlet being adapted to discharge fuel into the secondary venturi, said second fuel outlet having a springloaded check valve therein, the first fuel outlet being open at all times whereby fuel is discharged only into the first stage when the engine is accelerated at a reasonable rate.

'1 rumorson. 

